Computer-assisted microsurgery methods and equipment

ABSTRACT

Computer-assisted microsurgery equipment, of the type including an articulated tool support, with one of the ends being integral with a fixed reference system R c . The system comprises cameras for determining the tool coordinates in said fixed reference system R c , and an image data base wherein are recorded images from an imaging system in the image reference system R i . The inventions characterized by having at least two sensors integral with the fixed reference system R c  supplying an electrical signal depending on the patient reference position R p  in the fixed reference system R c , and a computer for matching the tool reference system R o  with the patient reference system R p  and the image reference system R i  according to data from the bidimensional sensor, cameras for determining the coordinates of the tool in the fixed reference system R c  and data from the image base. The computer supplies a signal for displaying the position of the tool in the image reference system R i  on a monitor and for controlling the position and shifting of said tool as a function of the control signals from the control unit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an installation for computer-assistedstereotactic microsurgery.

2. Description of the Related Art

Such installations are known in the state of the art. For example,French Patent FR 2651760 describes a method for the precise localizationof a lesion and a device for the implementation of this method. Theinvention relates to a device and a method for the precise localizationof a lesion. The method in accordance with the invention ischaracterized in that the organ to be examined is immobilized in thesame position as that of the biopsy to be performed, tomodensitometricaxial (XY) sections of the organ are performed through at least onetransparent rectangle fitted with three nonsymmetrical concurrent opaquethreads occupying determined positions in relation to the biopsyequipment, the lengths of the two segments (AB, AC) intercepted by saidopaque threads for a selected lesion section are measured, at least oneimage is taken in the specimen removal position, the traces of the threeopaque threads are reconstructed on said image and one transfers ontosaid image the lengths (AB, AC) of the measured segments in order todetermine the lesional baseline corresponding to the selected lesionalsection.

Implementation of this method entails complete immobilization of thepatient.

Another French patent published as number FR 2686499 describes a devicefor treating a target such as a lesion inside the body, using a markerelement implanted in or near the target to direct the treatment of saidtarget. This therapeutic device comprises:

means for treating the lesion,

lesion localization means, with the localization means being linked, forexample mechanically or electrically, to the therapeutic means,

means for calculating the position of the lesion relative to thetherapeutic means using the localization means,

means for activating the therapeutic means.

The localization means identify the localization of at least one markerelement implanted in the interior of the lesion. The calculation meanscalculate the position coordinates of the marker element (M0, M1, M2,M3) in relation to the therapeutic means which are used for thepositioning of the mobile therapeutic means in the space of any positionaccording to the X, Y, Z axes. This device enables precise treatment ofthe lesion.

Such a device requires intense presurgical preparation for itsimplementation.

French patent FR 2682778 describes a microscope for computer-assistedstereotactic microsurgery and a method for its operation. Thismicroscope comprises detectors that detect optical data, a positionidentification system and a process control device that evaluates thesignals from the said system. This system is an optics-based systemintegrated into the optical system of the microscope and it is providedwith a device that converts the signals output by the device into atwo-dimensional graphical representation.

Another patent of the prior art, patent PCT/FR090/00714, discloses aninstallation in which the principal reference system is linked to thepatient's bed. The patient is immobilized in relation to the bed by aretention helmet or equivalent means. This document of the prior artdiscloses that the system has marked positioning means 2 linked inrelation to the reference system R2 of the structures SNH and SR. Forexample, the head is fixed on the operating table.

This solution is not completely satisfactory because the retention meansreduce the possible routes of access and impose constraints that arerestrictive for the surgeon, who must assume that the position of thepatient is fixed definitively as of the beginning of the intervention.

In addition, the operating table never exhibits absolute mechanicalrigidity, and the correlation between the patient and the virtual imagesdoes not exhibit an adequate degree of precision for certaininterventions.

Patent WO92/06644 describes a radiotherapy installation with means forattaining concordance between the radiation sources and previouslyobtained images. This document does not mention the use of a referencesystem corresponding to the fixed-reference system of the applicant'sinvention, which is additionally not necessary given the applicationsenvisaged in this document of the prior art.

SUMMARY OF THE INVENTION

The object of the present invention is to resolve these drawbacks byproposing an installation of ergonomic use which makes it possible toseparate the image-acquisition phase and the phase involving theexploitation of the images for surgical purposes.

In the state of the art, the image-acquisition systems for diagnosticpurposes that do not require an intensive or traumatic interventioncannot be exploited for perioperative purposes. In fact, perioperativeimaging requires the use of stereotactic techniques which arerestrictive for the patient and for the operative personnel. Thesetechniques notably involve a painful phase involving the implantation ofa mechanical structure in the form of a frame which is indispensable foracquiring the images in relation to a known fixed reference system, toenable satisfactory calibration of the images, and to assure theimmobilization of the patient's head, or more generally of the operativezone, in relation to a given reference system.

The goal of the invention is to assure a correlation between the digitalimages obtained by means of a medical imaging system with the patient soas to provide the surgeon with the data intended to guide his operativestrategy in real time. Certain interventions require a precision of thecorrelation on the order of a millimeter or even less than a millimeter.

In order to attain this goal, the installation in accordance with theinvention has an absolute reference system which is the fixed referencesystem Rr linked to a structure totally independent of the patient or ofthe imaging or visualization system.

Another goal of the invention is to enable surgeons to carry out imageacquisition from a patient who is autonomous and not anesthetized,following a simplified procedure, at any time whatsoever of thehospitalization, or even in a different hospital facility, and possiblyto use several complementary imaging techniques.

The invention relates more specifically to an installation of the typecomprising an articulated tool-support, one end of which is integralwith a fixed reference system R_(c), with said system comprising meansfor determining the coordinates (position of a point and orientation ofa direction vector) of the tool in said fixed reference system R_(c), aswell as an image data base in which are recorded the images originatingfrom an imaging system in the image reference system R_(i). Theinstallation in accordance with the invention comprises at least twosensors integral with the fixed reference system R_(c) outputting anelectric signal that is a function of the position of the patientreference system R_(p) in the fixed reference system R_(c), and acomputer for implementation of correspondence between the tool referencesystem Ro and the patient reference system R_(p) and the image referencesystem R_(i) as a function of the data stemming from said sensor, meansfor determining the coordinates of the tool in said fixed referencesystem R_(c) and the data stemming from the image data base, saidcomputer outputting a signal for the visualization of the position ofthe tool in the image reference system R_(i) , on a control screen, andfor controlling the position and the displacements of the tool as afunction of control signals output by a control unit.

This installation enables processing of one or more images acquiredprior to the intervention, before the patient is transferred to thesurgical unit, and the exploiting in real time of the images in relationto the progression of the surgical intervention,

The fixed reference system is a totally independent reference system andis decoupled from the patient reference system as well as the imagereference system and the tool reference system. The fixed referencesystem is an absolute and permanent reference system. It is, forexample, linked to a structural element of the surgical unit, forexample the ceiling, the floor or a wall. This fixed reference system isselected in a manner so as to guarantee a permanent and stable referencesystem in which the various transformation matrices can be calculated inall situations, without limiting either the possible patientdisplacements or the possible tool displacements.

In accordance with a first variant, the sensors are constituted by atleast two acquisition cameras integral with the fixed reference systemR_(c) and positioned such that their field of observation contains thesurgical intervention zone.

Advantageously, the means for determining the coordinates of the tool insaid fixed reference system R_(c) are constituted by at least twoacquisition cameras integral with the fixed reference system R_(c) andpositioned such that their field of observation contains the mobilityspace of the tool.

In accordance with a preferred mode of implementation, the installationcomprises a geometrically defined trihedron, presenting at least fournoncoplanar punctiform light sources integral with the tool carrier,with the mobility space of said trihedron being contained in the fieldof vision of the acquisition cameras.

Advantageously, the installation additionally comprises a geometricallydefined trihedron, presenting at least four non-coplanar punctiformlight sources integral with the patient, with the mobility space of saidtrihedron being contained in the field of vision of the acquisitioncameras.

BRIEF DESCRIPTION OF THE DRAWINGS

Better comprehension of the invention will be gained from thedescription below which refers to the attached drawings in which:

FIGS. 1a-1d represent schematic views of the installation.

The installation in accordance with the invention comprises:

an articulated support (1);

a tool-carrier stage (2);

a set of three cameras (3, 4, 5);

reference trihedrons (21, 31);

a computer (8);

a device for storing digitized images (9);

a visualization screen (10).

The articulated support (1) comprises a base (11) integral with thefixed reference system R_(c) which is, for example, the ceiling of theoperating room.

The articulated support (1) is constituted in the described example by asystem of the "three parallel delta axes" type. It comprises a firstseries of three arms (12, 13, 14) connected to the base (11) byindependently controlled motors (15). The first series of three arms(12, 13, 14) is connected to a second series of arms (17, 18, 19) byball-and-socket joints (16). The ends of the arms (17 to 19) areintegral with a support (20) via rotational axes. The arms are spacedapart from each other by 120 degrees in a plane parallel to the base(11).

The end of the arms (17 to 19) is connected to a mechanism (20)comprising 3 rotational axes perpendicular in pairs, with the end ofthis latter rotational axis supporting a tool-carrier stage (2)comprising coupling means for a surgical instrument.

This support also comprises a trihedron (21) constituted by an assemblyof four light points (22 to 25), for example, electroluminscent diodes,the geometric positioning of which is known precisely.

The displacement of this trihedron (21) is acquired by the set ofcameras (3, 4, 5) which output an electric signal enabling thecalculation at any moment of the position of the center of gravity ofthe trihedron (21) and its orientation, in the fixed reference systemR_(c), and thus to determine the passage matrix between the fixedreference system R_(c) and the tool-carrier reference system R_(o).

According to one mode of implementation, the electroluminscent diodesare powered sequentially, with detection being implemented in asynchronous manner.

The patient (30) also carries a trihedron (31) that allows the set ofcameras (3, 4, 5) to output an electric signal enabling calculation atany moment of the position of the center of gravity of the trihedron(31) and its orientation, in the fixed reference system R_(c), and thusto determine the passage matrix between the fixed reference systemRk_(c) and the patient reference system R_(p).

The geometrically defined trihedron can also be implemented in the formof implants installed on the patient before acquisition of the images,and located at four unaligned points. In this case, these implants aremade of a material that allows detection by the imaging system(s)employed. The implants are, for example, made of titanium.

The method for using the installation for a surgical intervention is thefollowing:

The patient, after preparation, enters into a first room in which imageacquisition equipment is installed. In this room, one proceeds in aknown manner to the instrumentation of the patient, the acquisition ofthe raw images and verification of the images obtained. The images aredigitized and stored in an image data base. These images are thenprocessed on a work station, in the absence of the patient, bycalibration and segmentation of the images, indexing of the images andpossible programming of the operative trajectories and strategies.

The patient is then transferred to the operating room.

In the operating room, one proceeds successively:

to the preparation of the patient;

to the instrumentation of the tool-carrier device;

to the installation of the patient, retaining the instrumentationinstalled in the image-acquisition phase;

to the complementary instrumentation of the patient;

to the implementation of correspondence among the various referencesystems;

to the surgical intervention and the recording of the operative images.

Only the complementary instrumentation will be visible during thesurgical intervention, with the initial instrumentation installed duringthe imaging phase being hidden under the sheets or the fields.

The patient is then transferred out of the operating room while theoperative images are processed on a work station.

The image-acquisition procedure by the imaging system is morespecifically comprised of:

shaving the patient if the intention is to instrument the head;

possibly anesthetize the patient before transforming him to the imagingroom;

installing the trihedron (15) or the implants;

positioning the patient in the imaging system;

carrying out image acquisition;

verifying the images recorded in the image data base, notably withregard to the visibility of the reference frames on each of the imagesrecorded, the definition and the data required for the subsequentsurgical intervention;

removing the patient from the room.

The images are acquired by any known imaging means, for example, MRI,angiography, radiography, tomodensitometry, etc. The digitized imagesare stored in a data base which possibly can be accessed via a datanetwork from a remote site.

The recorded images are then processed by proceeding to:

the calibration of the images according to the imaging specificationsemployed;

the segmentation of the images for 2D/3D or 3D exploitation;

the possible indexing of the reference frames for the implementation ofcorrespondence;

the localization of the characteristic points of the images contained inthe image data base, for exploitation during the operative phase,notably by the determination of the targets, possible routes of accessand instrument trajectories, and possibly by the simulation of differentstrategies in 2D or 3D, and entry into the memory of the testedprogression axes.

After this image processing step and the virtual exploitation of theimage data base, the patient is transferred to the operating room.

In order for the surgeon to be able to exploit the previously acquireddata, it is necessary to know the position and the relative orientationof the axis of the tool in relation to the images, in the intermediatereference frame corresponding to the intervention zone on the patient.

For this purpose, the invention enables the implementation ofcorrespondence between the images acquired and linked to the patient,with the tool. The localization should be possible no matter theposition of the tool and the patient.

The trihedron (21) that localizes the position of the tool is fixed in aremovable or non-removable manner on the tool-carrier base. Theattachment means should preferably not be articulated so as to guaranteepermanence to the position of the trihedron (21) in relation to the toolsupport. Locking can be implemented with a clip connection.

Localization of the patient can be implemented in various manners: byinstalling a normalized rigid trihedron, or by installing unalignedimplants, or by designating characteristics points of the surface of thepatient, close to the operative zone, with a localization stylus.

This latter solution is comprised of employing a stylus-shaped pointer(32), carrying two reference points detectable by the camera system, andallowing designation, and thus input into the memory of the position ofdifferent characteristic points of the patient, of which it is possibleto follow the displacements by shape recognition. The characteristiczones are, for example, the nose, the corners of the eyes or the chin.

Such a sensor (32) has a stylus shaped body terminated by a pointingzone (35) and comprising at least two light points (33, 34) enablingdetermination of the position and the orientation of the sensor (32) byanalysis of the signals output by the cameras (3, 4, 5).

The implementation of concordance between the reference systems will beexplained in greater detail below.

To facilitate comprehension, the following designations will beemployed:

^(a) P a defined point in the reference frame R_(a) ;

^(a) T_(b) the matrix of homogeneous transformation (4 lines, 4 columns)allowing expression in reference frame R_(a) of the coordinates of adefined point in reference frame R_(b), by the relation ^(a) P=^(a)T_(b) ^(b) P.

In addition, the various reference frames cited are:

R_(o) Reference frame of the tool;

R_(i) Reference frame of the image;

R_(c) Reference frame of the cameras;

R_(pr) Reference frame of the sensor;

R_(pg) Gross reference frame of the patient;

R_(pc) Corrected reference frame of the patient;

R_(mi) Geometric reference frame defined by at least 4 unaligned points(i variant of 1 to n);

R_(m1) Geometric reference frame linked to the tool

R_(m2) Geometric reference frame linked to the patient.

In addition, ^(pr) S will designate the surface defined by a set ofpoints P, acquired in the sensor reference frame R_(pr) and ^(i) S thesurface defined by a set of points P_(j) acquired in the image referenceframe R_(i).

Step 1: Implementation of concordance between the image reference frameand the patient reference frame

The first step in the implementation of concordance between thereference systems consists of calculating the matrix ^(i) T_(p/pc) ofpassage between the image reference frame and the patient referenceframe.

In accordance with one example of implementation of the installation,one uses a sensor (32) in order to mark known conspicuous points in theimage reference frame R_(i). The coordinates of the ends of the sensor(32) are known by construction, and by processing of the data output bythe cameras (3, 4, 5) detecting the light points (33, 34) carried by thesensor.

It is thus possible to express the coordinates of the end (35) of thesensor (32) in the reference frame of the camera by the relation:

    .sup.c P.sub.sensor end =.sup.c T.sub.pr.sup.pr P.sub.sensor end

and thus to calculate the matrix of passage between the camera referencesystem and the sensor reference system.

One uses, in addition, inserts or a trihedron (31) comprising in eithercase four unaligned points identifiable by the cameras (3 to 5) anddefining the reference frame R_(pc) of the patient.

These points ^(P) _(j) are known in the image reference frame R_(i) andare measured with the sensor (32), in the sensor reference frame R_(pr)in which their coordinates are ^(pr) P_(j). When the end of the sensorpoints on one of the points of the trihedron (31) or on one of theinserts, one has an identity relation between the two coordinates:

    .sup.pr.sub.j =.sup.pr R.sub.sensor end

The transformation ^(i) T_(pr) is thus determined by a relation betweenthe points ^(i) P_(j) from the image data base and the points ^(pc)P_(j) measured with the sensor. One uses the intermediate referenceframe kR_(m2) fixed by principle of use, in relation to the referenceframe R_(pc) and one determines the matrix of transformation ^(i)T_(m2). This matrix ^(i) T_(m2) is determined by a relation between thepoints ^(i) P_(j) of the image data base and the points ^(m2) P_(j)measured with the sensor.

In fact, when the end of the sensor (32) points on a point P_(j), thefollowing relation is verified:

    .sup.m2 P.sub.j =.sup.m2 T.sub.c (t).sup.c T.sub.pr (t).sup.pr P.sub.sensor end

and one then determines ^(i) T_(m2) by the least squares method:##EQU1##

According to an implementation variant, one avoids installation of atrihedron (31) or inserts, by using a surface correspondence method.

This requires two consecutive steps:

The first step consists of marking 4 conspicuous point on the patient(for example, the nose, the eyes, etc.). One is then in a situationsimilar to the preceding variant because one has available non-coplanarpoints P_(j), the coordinates ^(i) P_(j) of which are known in the imagereference frame R_(i). The transformation ^(i) T_(pg) is determined by arelation between the points ^(i) P_(j) from the image data base and thepoints ^(pg) P_(j) measured with the sensor (32).

As above, one uses the intermediate reference frame R_(m2) fixed inrelation to the reference frames RK_(pg) andR_(pc).

One then obtains a "gross" transformation (^(i) T_(m2))_(g) which allowsone to obtain a precision on the order of several millimeters which isinsufficient for clinical use.

The second step consists of defining a corrected patient reference frameR_(pc) by marking a multiplicity of conspicuous points in the vicinityof the intervention zone, using the sensor (32).

This operation makes it possible to bring into correspondence twosurface.

the real surface of the patient, defined by the acquisition made withthe sensor ^(pr) S (^(pr) P_(j)) with n≧j≧4, with the resolutionimproving as the magnitude of n increases;

the surface ^(i) S linked to the image of the patient closest to thereal surface defined in the image reference frame, and using the grosstransformation (^(i) T_(m2))_(g) in selecting for this purpose only apart of the image data bank ^(pr) S{^(pr) P_(j) } with n≧j≧4.

One then has the following relation:

    .sup.m2 P.sub.j =.sup.m2 T.sub.c (t).sup.c T.sub.pr (t).sup.pr P.sub.sensor end

with

    .sup.pr P.sub.sensor end =.sup.pr P.sub.j

and one then determines ^(i) T_(m2) by the least squares method:

    MinΣ∥(.sup.i S{P.sub.j }-.sup.i T.sub.m2.sup.m2 S{.sup.m2 P.sub.j }).sup.2 ∥with n≧j≧4

Step 2: Implementation of concordance between the tool reference frameand the fixed reference frame

The following step of implementation of concordance between thereference systems consists of calculating the matrix ^(c) T_(o) ofpassage between the tool reference frame and the fixed reference frame.

The transformation ^(m2) T_(o) giving the relation between the toolreference frame R_(o) and the fixed reference frame R_(m1) is known byconstruction.

The coordinates of a point ^(o) P in the reference frame R_(o) can beexpressed in the reference frame R_(m1) by the relation:

    .sup.m1 P=.sup.m1 T.sub.o.sup.o P

The transformation ^(c) T_(m1) giving the relation between the fixedreference frame R_(m1) and the reference frame R_(c) is known in realtime by infrared measurement. The coordinates of a point ^(m1) P in thereference frame R_(m1) can be expressed in the reference frame R_(c) bythe relation:

    .sup.c P=.sup.c T.sub.m2 (t).sup.m1p

The coordinates of a point ^(o) P linked to the tool can thus beexpressed in real time in the fixed reference frame of measurement R_(c)by the relation:

    .sup.c P=.sup.c T.sub.m1 (t).sup.m1 T.sub.o.sup.o P

Since the reference frame R_(o) is defined by the trihedron (21), onethus obtains the relation in real time between the tool reference frameR_(o) and the camera reference frame R_(c).

Resolution of the equations enabling calculation of the transformationmatrices

The fixed reference frame R_(m1) is defined by at least 4 non-coplanarpoints ^(m1) P₁ to ^(m1) P₄.

The cameras (3 to 5) detect these four points in the camera referencesystem, in which their coordinates are ^(c) P₁ to ^(c) P₄.

One looks for the relation ^(c) T_(m1) such that:

    .sup.c P.sub.j =.sup.c T.sub.m1.sup.m1 P.sub.j

    in which

    j=1 to 4

Theoretically,

    |.sup.c P.sub.j -.sup.c T.sub.m1.sup.m1 P.sub.j |=0

Thus, one looks for ^(c) T_(m1) that minimizes errors, from which:##EQU2##

The minimum is determined by derivation.

^(c) T_(m1) is a homogeneous 4×4 matrix with 12 conspicuous elements##EQU3##

One derives the relation ##EQU4## and one obtains a system of 3×4=12equations with 12 unknowns for k=1 to 3: k being the line index

for 1=1 to 4, 1 being the column index ##EQU5##

Since ##EQU6## one can deduce the following relations: ##EQU7##

In this equation, one has:

T_(k1)

T_(k1)

T_(k2)

T_(k3)

T_(k4)

The equation system obtained by ##EQU8## with k=1 to 3 and 1=1 to 4decomposes into 3 independent subsystems ##EQU9##

The resolution of this equation system is performed by an algorithmknown by the computer of the installation in accordance with theinvention, which will not be discussed in greater detail in the contextof the present description, since the expert in the field is in aposition to implement suitable data processing solutions.

Step 3: Implementation of concordance between the image reference frameand the camera reference frame

The step following the implementation of concordance between thereference systems consists of calculating in real time the matrix ^(m2)T_(i) (t) of passage between the reference frame R_(m2) linked to thepatient with the image reference frame R₁.

The transformation ^(c) T_(pr) giving the relation between the referenceframe R_(pr) of the sensor (32) and the camera reference frame R_(c) isknown in real time by infrared measurement.

The coordinates of a point ^(pr) P in the reference frame R_(pr) can beexpressed in the reference frame R_(c) by the relation:

    .sup.c P=.sup.c T.sub.pr(t).sup.pr P

The transformation ^(c) T_(m2) giving the relation between the fixedreference frame R_(m2) and the reference frame R_(c) is known in realtime by infrared measurement. The coordinates of a point ^(m2) P in thereference frame R_(m2) can be expressed in the reference frame R_(c) bythe relation:

    .sup.c P=.sup.c T.sub.m2 (t).sup.m2 P

in which ^(cpl) T_(m2) (t) is determined in a manner similar to ^(c)T_(m1) (t).

The coordinates of the end of the sensor (32) ^(c) P_(sensor) end areknown in the reference frame R_(pr) by construction.

They can be expressed by the reference:

    .sup.c P.sub.sensor end =.sup.c T.sub.pr (t).sup.pr P.sub.sensor end

Thus, they can be expressed in the reference frame R_(m2) by therelation:

    .sup.m2 P.sub.sensor end =.sup.m2 T.sub.c.sup.c T.sub.pr (t).sup.pr P.sub.sensor end

Step 4: Implementation of concordance between the image reference frameand the tool reference frame

The final step in the implementation of concordance consists ofdetermining the relation between the reference frame R_(o) imagereference frame R₁.

For this, one knows:

Step 2: the position of the tool in the reference frame of the camerasby the transformation ^(m1) T_(o).sbsb.- (known by construction) and^(c) T_(m1) (t) (determined in real time by infrared measurement);

Step 3: the correlation between the fixed reference frame R_(m2) and theimage reference frame R₁ by the transformation ^(i) T_(m2), determinedduring the implementation of correspondence.

The position of the reference frame R_(m2) in relation to the fixedreference frame R_(c) by the transformation ^(m2) T_(c)(t) which is theinverse of ^(c) T_(m2)(t), determined in real time by infraredmeasurement.

Thus, one obtains the transformation

    .sup.i T.sub.o(t) =.sup.i T.sub.m2.sup.m2 T.sub.c(t).sup.c T.sub.m1(t).sup.m1 T.sub.o

enabling the display in real time of the section corresponding to thepoint of interest.

One also obtains the transformation ^(o) T_(i)(t), inverse of ^(i)T_(o)(t).sbsb.-, making it possible to automatically control the tool inreal time in relation to a target defined in the image data base.

The invention is described above as a nonlimitative example. It isobvious that the Expert in the Field could propose diverse variantswithout going beyond the scope of the invention.

I claim:
 1. A computer-assisted microsurgery installation, comprising:(a) an articulated tool support, one end of which is integral with a fixed reference frame R_(c) ; (b) an image data base comprising images in an image reference frame R_(i) ; (c) at least two sensors, integral with the fixed reference frame R_(c), supplying a signal that is a function of the position of a reference frame R_(p) of a patient in the fixed reference frame R_(c) ; (d) a computer adapted to:(1) determine correspondence of a reference frame R_(o) of the tool with the patient reference frame R_(p) and the image reference frame R_(i) as a function of the signal from the at least two sensors; (2) output a display signal for visualization of position of the tool in the image reference frame R_(i) on a control screen; and (3) control position and displacements of the tool as a function of control signals originating from a control unit, wherein the fixed reference frame R_(c) is independent of the patient reference frame R_(p) and of the image reference frame R_(i) ; and (e) means for determining coordinates of the tool in the fixed reference system R_(c) based on data from the image data base.
 2. The installation of claim 1, wherein the at least two sensors comprise at least two acquisition cameras integral with the fixed reference system R_(c) and positioned such that their field of observation includes a surgical intervention zone.
 3. The installation of claim 2, further comprising a first geometrically defined trihedron, presenting at least four non-coplanar punctiform light sources integral with the tool, with the mobility space of the first trihedron being contained in the fields of vision of the acquisition cameras.
 4. The installation of claim 3, further comprising a second geometrically defined trihedron, presenting at least four non-coplanar punctiform light sources integral with the patient, with the mobility space of the second trihedron being contained in the fields of vision of the acquisition cameras during an entire operative phase.
 5. The installation of claim 1, wherein the means for determining coordinates of the tool in the fixed reference system R_(c) comprises at least two acquisition cameras integral with the fixed reference system R_(c) and positioned such that their field of observation includes the mobility space of the tool.
 6. The installation of claim 5, further comprising a first geometrically defined trihedron, presenting at least four non-coplanar punctiform light sources integral with the tool, with the mobility space of the first trihedron being contained in the fields of vision of the acquisition cameras.
 7. The installation of claim 6, further comprising a second geometrically defined trihedron presenting at least four non-coplanar punctiform light sources integral with the patient, with the mobility space of the second trihedron being contained in the fields of vision of the acquisition cameras during an entire operative phase.
 8. The installation of claim 1, further comprising an additional sensor comprising a pointing end and at least two light points, the positions of which in relation to the pointing end are determined geometrically by placing the additional sensor within the fields of vision of the at least two sensors.
 9. The installation of claim 1, wherein:the at least two sensors comprise at least two acquisition cameras integral with the fixed reference system R_(c) and positioned such that their field of observation includes a surgical intervention zone and the mobility space of the tool; and further comprising: a first geometrically defined trihedron, presenting at least four non-coplanar punctiform light sources integral with the tool, with the mobility space of the first trihedron being contained in the fields of vision of the acquisition cameras; a second geometrically defined trihedron, presenting at least four non-coplanar punctiform light sources integral with the patient, with the mobility space of the second trihedron being contained in the fields of vision of the acquisition cameras during an entire operative phase; and an additional sensor comprising a pointing end and at least two light points, the positions of which in relation to the pointing end are determined geometrically by placing the additional sensor within the fields of vision of the acquisition cameras.
 10. A method for performing microsurgery using a microsurgery tool, comprising the steps of:(a) determining the position of the tool in a reference frame R_(c) of a camera by a transformation ^(m1) T_(c), giving the relation between a reference frame R_(o) of the tool and a fixed reference frame R_(m1), and a transformation ^(c) T_(m1It)), giving the relation between the camera reference frame R_(c) and the fixed reference frame R_(m1) determined in real time by optical measurement; (b) determining a transformation ^(i) T_(m2) giving the relation between an image reference frame R_(i) and a fixed reference frame R_(m2) ; (c) determining the position of the fixed reference frame R_(m2) in relation to the camera reference frame R_(c) by a transformation ^(m2) T_(c)(t) determined in real time by optical measurement; (d) calculating a transformation ^(i) T_(o)(t)=^(i) T_(m2) ^(m2) T_(o)(t)^(c) T_(m1)(t)^(m1) T_(o), giving the relation between the image reference frame R_(i) and the tool reference frame R_(o), to display in real time a section corresponding to a point of interest indicating the position of the tool in relation to a prerecorded image; and (e) performing the microsurgery based on the real-time display of the section.
 11. A method for controlling a microsurgery tool in relation to an image data base, comprising the steps of:(a) determining the position of the tool in a reference frame R_(c) of a camera by a transformation ^(m1) T_(o), giving the relation between a reference frame R_(o) of the tool and a fixed reference frame R_(m1), and a transformation ^(c) T_(m1)(t), giving the relation between the reference flame R_(c) and the fixed reference frame R_(m1) determined in real time by optical measurement; (b) determining a transformation ^(i) T_(m2) giving the relation between an image reference frame R_(i) and a fixed reference frame R_(m2) ; (c) determining the position of the fixed reference frame R_(m2) in relation to the reference frame R_(c) by a transformation ^(m2) T_(c)(t) determined in real time by optical measurement; (d) calculating a transformation ^(i) T_(o)(t)=^(i) T_(m2) ^(m2) T_(c)(t)^(c) T_(m11)(t)^(m1) T_(o), giving the relation between the image reference frame R_(i) and the tool reference frame R_(o) ; (e) calculating a transformation ^(o) T_(i)(t), which is an inverse of the transformation ^(i) T_(o)(t) ; and (f) automatically controlling the tool in real time in relation to a target defined in the image data base using the transformation ^(o) T_(i)(t). 